The present disclosure relates to a multibubble injection type DAF (Dissolved Air Flotation) water treatment apparatus, and more particularly, to a multibubble injection type DAF (Dissolved Air Flotation) water treatment apparatus which supplies fine bubbles injected through injection of saturated water to a lower area of a separation zone as well as a lower area of a contact zone of a flotation basin, thereby improving removal efficiency of flocs.
In general, a water treatment apparatus is an apparatus which produces fresh water using seawater to utilize the fresh water as water for living, eating or industrial use or properly treat raw water to purify waste water. Such a water treatment apparatus includes a device for removing foreign matters mixed in raw water.
As a unit process for removing foreign matters, there is DAF (Dissolved Air Flotation). The dissolved air flotation is a widely applied technology for various water treatment and sewage treatment processes or a pretreatment process for seawater desalination facilities. The dissolved air flotation is a technology of putting a coagulant, an aid coagulant, a pH regulator and so on in feed water to be treated in order to coagulate suspended particles, which is difficult to be removed through precipitation, such as alga and organic compounds, contained in feed water, injecting micro bubbles into the coagulated matters to combine the micro bubbles with the suspended particles, and floating and removing the suspended particles. In general, a DAF water treatment apparatus includes a mixing and coagulation basin (or a mixing basin), a flocculation basin and a flotation basin, and the flotation basin is divided into a contact zone and a separation zone.
Referring to FIG. 1, a related DAF water treatment apparatus will be described. First, when a coagulant is inserted into feed water to flocculate suspended particles of low density, which is contained in the feed water, in a mixing and coagulation basin 1.
“Floc” means a large mass that fine particles, such as suspended solids, organic matters and inorganic matters, contained in the raw water are flocculated by the coagulant, and generally means a collected thing formed by flocculation of particles of 0.1 μm or more. Flocs of a small size or density which cannot be removed through filtration or precipitation are floated onto the surface of water to be removed using the dissolved air flotation water treatment apparatus.
The flocs generated and grown up in the mixing and coagulation basin 1 flow into a flotation basin located at a rear end. The flocs flown into a contact zone 2 are floated to the surface of water by colliding and combining with fine bubbles injected from a lower part of the contact zone 2, and then, are removed through a scum removal device in a separation zone 3. In connection with the summary of the dissolved air flotation apparatus, please refer to FIG. 1 of U. S. Patent Publication No. 2012-0193294 entitled ‘Dissolved gas flotation pressure reduction nozzle’ published on Aug. 2, 2012.
The related DAF water treatment apparatus separates some of treated water which is an end product by a pipe and supplies compressed air of 4 to 7 bars to saturate the treated water. So, a rapid drop of pressure occurs, and then, micro bubbles are supplied to the contact zone 2 through a nozzle 4 mounted at the lower part of the contact zone 2.
In the meantime, formation and growing of the flocs in the mixing and coagulation basin 1 are influenced by raw water conditions, such as seawater temperature, polluted states and the containing degree of suspended matters, and coagulation conditions, such as stirring intensity, residence time and amounts of added chemicals. Accordingly, the flocs cannot perfectly develop in the mixing and coagulation basin 1, and hence, fine flocs are formed and cannot float properly or grow up into large flocs inside the separation zone 3 located at the downstream of the contact zone 2.
Because all of recycle flows in which compressed air is saturated are supplied only to the contact zone 2, the flocs which grow too late at the downstream of the mixing and coagulation basin 1 do not have a sufficient opportunity to come into contact with the micro bubbles and flow into the rear end of the system. Therefore, the related dissolved air flotation system has a disadvantage in that quality of the treated water is deteriorated and it has influences on the following processes.